Can you get a 22mag cylinder for a FIE 22lr?

There have been a few revolvers made with interchangeable 22LR and 22 magnum cylinders. However, you cannot add a cylinder unless made for that from the start (22 mag has a larger bore diameter). FIE was the importer, not the maker of arms with their name on it- and they have been out of business for several years. IF you have a "convertable" .22, you may find a cylinder through Numrich, Shotgun News, or similar dealers in used parts.